alt Hacker NewsReactivity is updating the DOM whenever the underlying data is updated. That's one of the most basic reason for existence of all js frameworks. There's TC39 Signals proposal to bring that natively, but for now as said above the choice is either use a framework or recreate one. It's surprisingly easy nowadays using Proxy.
How I've done it is to use some kind of observer pattern, where you register listeners to state changes.
Whenever state is updated, the listeners are all called with the updated state and can update the UI and what not based on the new state.
I haven't profiled this and compared it to frameworks, but feels adequate for the relatively simple UIs I've done.